Device manufacturing method, top coat material and substrate

ABSTRACT

In immersion lithography, to avoid internal reflections in the final element of the projection system, immersion fluid and topcoat, the thicknesses, d l , d tc  and d r , and refractive indices, n l , n tc  and n r , of the immersion fluid, topcoat and resist may meet the following criteria:
 
 n   l   ≦n   tc   ≦n   r  
 
 d   l   &gt;˜5.λ 
 
 d   tc   ≦˜5.λ

FIELD

The present invention relates to a method for manufacturing a device, atopcoat material and a substrate provided with a topcoat.

BACKGROUND

A lithographic apparatus is a machine that applies a desired patternonto a substrate, usually onto a target portion of the substrate. Alithographic apparatus can be used, for example, in the manufacture ofintegrated circuits (ICs). In that instance, a patterning device, whichis alternatively referred to as a mask or a reticle, may be used togenerate a circuit pattern to be formed on an individual layer of theIC. This pattern can be transferred onto a target portion (e.g.comprising part of, one, or several dies) on a substrate (e.g. a siliconwafer). Transfer of the pattern is typically via imaging onto a layer ofradiation-sensitive material (resist) provided on the substrate. Ingeneral, a single substrate will contain a network of adjacent targetportions that are successively patterned. Known lithographic apparatusinclude so-called steppers, in which each target portion is irradiatedby exposing an entire pattern onto the target portion at one time, andso-called scanners, in which each target portion is irradiated byscanning the pattern through a radiation beam in a given direction (the“scanning”-direction) while synchronously scanning the substrateparallel or anti-parallel to this direction. It is also possible totransfer the pattern from the patterning device to the substrate byimprinting the pattern onto the substrate.

It has been proposed to immerse the substrate in the lithographicprojection apparatus in a liquid having a relatively high refractiveindex, e.g. water, so as to fill a space between the final element ofthe projection system and the substrate. The point of this is to enableimaging of smaller features since the exposure radiation will have ashorter wavelength in the liquid. (The effect of the liquid may also beregarded as increasing the effective NA of the system and alsoincreasing the depth of focus.) Other immersion liquids have beenproposed, including water with solid particles (e.g. quartz) suspendedtherein.

However, submersing the substrate or substrate and substrate table in abath of liquid (see, for example, U.S. Pat. No. 4,509,852, herebyincorporated in its entirety by reference) means that there is a largebody of liquid that must be accelerated during a scanning exposure. Thisrequires additional or more powerful motors and turbulence in the liquidmay lead to undesirable and unpredictable effects.

One of the solutions proposed is for a liquid supply system to provideliquid on only a localized area of the substrate and in between thefinal element of the projection system and the substrate (the substrategenerally has a larger surface area than the final element of theprojection system). One way which has been proposed to arrange for thisis disclosed in PCT patent application WO 99/49504, hereby incorporatedin its entirety by reference. As illustrated in FIGS. 2 and 3, liquid issupplied by at least one inlet IN onto the substrate, preferably alongthe direction of movement of the substrate relative to the finalelement, and is removed by at least one outlet OUT after having passedunder the projection system. That is, as the substrate is scannedbeneath the element in a −X direction, liquid is supplied at the +X sideof the element and taken up at the −X side. FIG. 2 shows the arrangementschematically in which liquid is supplied via inlet IN and is taken upon the other side of the element by outlet OUT which is connected to alow pressure source. In the illustration of FIG. 2 the liquid issupplied along the direction of movement of the substrate relative tothe final element, though this does not need to be the case. Variousorientations and numbers of in- and out-lets positioned around the finalelement are possible, one example is illustrated in FIG. 3 in which foursets of an inlet with an outlet on either side are provided in a regularpattern around the final element.

Various different materials have been proposed for use as the immersionliquid, i.e. the liquid that fills a space between the projection systemand the substrate, such as ultra-pure water. Ultra-pure water interactschemically with resists used in “dry” lithography thus leading to thedevelopment of new resists for immersion lithography and/or the use of aso-called topcoat between the resist and the immersion liquid.

SUMMARY

Besides water, other liquids with higher refractive indexes, e.g. >1.6,may be used in immersion lithography, including sulfuric acid andsuspensions of nano-particles, e.g. of Al₂O₃.

Accordingly, it would advantageous, for example, to provide a topcoatthat is compatible with immersion fluids having a refractive index ofgreater than about 1.6.

According to an aspect of the invention, there is provided a devicemanufacturing method, comprising:

projecting a patterned beam of radiation through a liquid onto a resistprovided on a substrate, wherein

a topcoat layer is provided between the resist and the liquid, thetopcoat layer having a thickness that is less than or equal to aboutfive times the wavelength of the radiation of the patterned beam,

the liquid has a thickness that is greater than or equal to about fivetimes the wavelength of the radiation of the patterned beam, and

the liquid, the topcoat and the resist have respectively, first, secondand third refractive indices, the first refractive index being less thanor equal to the second refractive index and the second refractive indexbeing less than or equal to the third refractive index.

According to another aspect of the invention, there is provided a devicemanufacturing method, comprising:

projecting a patterned beam of radiation through a liquid onto a resistprovided on a substrate, wherein

a topcoat layer is provided between the resist and the liquid, thetopcoat has a thickness substantially equal to

$\frac{\left( {m - \frac{1}{2}} \right)\lambda}{2 \cdot n_{tc} \cdot \left( {1 - {\sin^{2}\beta}} \right)},$wherein

${{\sin\;\beta} = {{NA} \cdot \frac{n_{l}}{n_{r}}}},$m=1, 2, 3, etc., λ is the wavelength of the radiation of the patternedbeam, NA is the numerical aperture at the substrate, n_(l) is therefractive index of the liquid, n_(tc) is the refractive index of thetopcoat, and n_(r) is the refractive index of the resist;

the liquid has a thickness that is greater than or equal to about fivetimes λ,

the resist has a thickness in the range of from half to one times λ, and

n_(l) is less than or equal to n_(tc), n_(tc) is less than or equal ton_(r), and n_(tc) is about equal to the square root of the product ofn_(l) and n_(r).

According to another aspect of the invention, there is provided a devicemanufacturing method, comprising:

projecting a patterned beam of radiation through a liquid onto a resistprovided on a substrate, wherein a topcoat layer is provided between theresist and the liquid, the topcoat comprising a suspension ofnano-particles.

According to an aspect of the invention, there is provided a devicemanufacturing method, comprising:

projecting a patterned beam of radiation through a liquid onto a resistprovided on a substrate, wherein a topcoat layer is provided between theresist and the liquid and a primer layer is provided between the resistand the topcoat, the primer layer having a thickness less than thewavelength of the radiation of the patterned beam.

According to an aspect of the invention, there is provided a substrate,comprising:

a surface substantially covered by a resist that can be exposed byradiation; and

a topcoat layer substantially covering the resist, the topcoat layerhaving a thickness less than or equal to about five times the wavelengthof the radiation,

wherein the topcoat and the resist have respectively, first and secondrefractive indices, the first refractive index being less than or equalto the second refractive index.

According to an aspect of the invention, there is provided a substrate,comprising:

a surface substantially covered by a resist that can be exposed byradiation;

a topcoat layer substantially covering the resist; and

a primer layer provided between the resist and the topcoat layer, theprimer layer having a thickness less than the wavelength of theradiation.

According to another aspect of the invention, there is provided asubstrate, comprising:

a surface substantially covered by a resist that can be exposed byradiation, the resist having a thickness in the range of from half toone times the wavelength; and

a topcoat layer substantially covering the resist, the topcoat layerhaving a thickness of about one quarter of the wavelength,

wherein the topcoat and the resist have respectively, first and secondrefractive indices, the first refractive index being less than or equalto the second refractive index.

According to another aspect of the invention, there is provided asubstrate, comprising:

a surface substantially covered by a resist that can be exposed byradiation; and

a topcoat layer substantially covering the resist, the topcoatcomprising a suspension of nano-particles.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of exampleonly, with reference to the accompanying schematic drawings in whichcorresponding reference symbols indicate corresponding parts, and inwhich:

FIG. 1 depicts a lithographic apparatus according to an embodiment ofthe invention;

FIGS. 2 and 3 depict a liquid supply system for use in a lithographicprojection apparatus;

FIG. 4 depicts another liquid supply system for use in a lithographicprojection apparatus;

FIG. 5 depicts a liquid supply system for use in an embodiment of theinvention;

FIG. 6 depicts different media through which a patterned beam passesnear the substrate in an embodiment of the invention;

FIG. 7 depicts the different media through which a patterned beam passesnear the substrate in another embodiment of the invention; and

FIG. 8 depicts the different media through which a patterned beam passesnear the substrate in yet another embodiment of the invention.

DETAILED DESCRIPTION

FIG. 1 schematically depicts a lithographic apparatus according to oneembodiment of the invention. The apparatus comprises:

-   -   an illumination system (illuminator) IL configured to condition        a radiation beam PB (e.g. UV radiation or DUV radiation).    -   a support structure (e.g. a mask table) MT constructed to        support a patterning device (e.g. a mask) MA and connected to a        first positioner PM configured to accurately position the        patterning device in accordance with certain parameters;    -   a substrate table (e.g. a wafer table) WT constructed to hold a        substrate (e.g. a resist-coated wafer) W and connected to a        second positioner PW configured to accurately position the        substrate in accordance with certain parameters; and    -   a projection system (e.g. a refractive projection lens system)        PL configured to project a pattern imparted to the radiation        beam PB by patterning device MA onto a target portion C (e.g.        comprising one or more dies) of the substrate W.

The illumination system may include various types of optical components,such as refractive, reflective, magnetic, electromagnetic, electrostaticor other types of optical components, or any combination thereof, fordirecting, shaping, or controlling radiation.

The support structure supports, i.e. bears the weight of, the patterningdevice. It holds the patterning device in a manner that depends on theorientation of the patterning device, the design of the lithographicapparatus, and other conditions, such as for example whether or not thepatterning device is held in a vacuum environment. The support structurecan use mechanical, vacuum, electrostatic or other clamping techniquesto hold the patterning device. The support structure may be a frame or atable, for example, which may be fixed or movable as required. Thesupport structure may ensure that the patterning device is at a desiredposition, for example with respect to the projection system. Any use ofthe terms “reticle” or “mask” herein may be considered synonymous withthe more general term “patterning device”.

The term “patterning device” used herein should be broadly interpretedas referring to any device that can be used to impart a radiation beamwith a pattern in its cross-section such as to create a pattern in atarget portion of the substrate. It should be noted that the patternimparted to the radiation beam may not exactly correspond to the desiredpattern in the target portion of the substrate, for example if thepattern includes phase-shifting features or so called assist features.Generally, the pattern imparted to the radiation beam will correspond toa particular functional layer in a device being created in the targetportion, such as an integrated circuit.

The patterning device may be transmissive or reflective. Examples ofpatterning devices include masks, programmable mirror arrays, andprogrammable LCD panels. Masks are well known in lithography, andinclude mask types such as binary, alternating phase-shift, andattenuated phase-shift, as well as various hybrid mask types. An exampleof a programmable mirror array employs a matrix arrangement of smallmirrors, each of which can be individually tilted so as to reflect anincoming radiation beam in different directions. The tilted mirrorsimpart a pattern in a radiation beam which is reflected by the mirrormatrix.

The term “projection system” used herein should be broadly interpretedas encompassing any type of projection system, including refractive,reflective, catadioptric, magnetic, electromagnetic and electrostaticoptical systems, or any combination thereof, as appropriate for theexposure radiation being used, or for other factors such as the use ofan immersion liquid or the use of a vacuum. Any use of the term“projection lens” herein may be considered as synonymous with the moregeneral term “projection system”.

As here depicted, the apparatus is of a transmissive type (e.g.employing a transmissive mask). Alternatively, the apparatus may be of areflective type (e.g. employing a programmable mirror array of a type asreferred to above, or employing a reflective mask).

The lithographic apparatus may be of a type having two (dual stage) ormore substrate tables (and/or two or more support structures). In such“multiple stage” machines the additional tables may be used in parallel,or preparatory steps may be carried out on one or more tables while oneor more other tables are being used for exposure.

Referring to FIG. 1, the illuminator IL receives a radiation beam from aradiation source SO. The source and the lithographic apparatus may beseparate entities, for example when the source is an excimer laser. Insuch cases, the source is not considered to form part of thelithographic apparatus and the radiation beam is passed from the sourceSO to the illuminator IL with the aid of a beam delivery system BDcomprising, for example, suitable directing mirrors and/or a beamexpander. In other cases the source may be an integral part of thelithographic apparatus, for example when the source is a mercury lamp.The source SO and the illuminator IL, together with the beam deliverysystem BD if required, may be referred to as a radiation system.

The illuminator IL may comprise an adjuster AD for adjusting the angularintensity distribution of the radiation beam. Generally, at least theouter and/or inner radial extent (commonly referred to as σ-outer andσ-inner, respectively) of the intensity distribution in a pupil plane ofthe illuminator can be adjusted. In addition, the illuminator IL maycomprise various other components, such as an integrator IN and acondenser CO. The illuminator may be used to condition the radiationbeam, to have a desired uniformity and intensity distribution in itscross-section.

The radiation beam PB is incident on the patterning device (e.g., mask)MA, which is held on the support structure (e.g., mask table) MT, and ispatterned by the patterning device. Having traversed the patterningdevice MA, the radiation beam PB passes through the projection systemPL, which focuses the beam onto a target portion C of the substrate W.With the aid of the second positioner PW and position sensor IF (e.g. aninterferometric device, linear encoder or capacitive sensor), thesubstrate table WT can be moved accurately, e.g. so as to positiondifferent target portions C in the path of the radiation beam PB.Similarly, the first positioner PM and another position sensor (which isnot explicitly depicted in FIG. 1) can be used to accurately positionthe patterning device MA with respect to the path of the radiation beamPB, e.g. after mechanical retrieval from a mask library, or during ascan. In general, movement of the support structure MT may be realizedwith the aid of a long-stroke module (coarse positioning) and ashort-stroke module (fine positioning), which form part of the firstpositioner PM. Similarly, movement of the substrate table WT may berealized using a long-stroke module and a short-stroke module, whichform part of the second positioner PW. In the case of a stepper (asopposed to a scanner) the support structure MT may be connected to ashort-stroke actuator only, or may be fixed. Patterning device MA andsubstrate W may be aligned using patterning device alignment marks M1,M2 and substrate alignment marks P1, P2. Although the substratealignment marks as illustrated occupy dedicated target portions, theymay be located in spaces between target portions (these are known asscribe-lane alignment marks). Similarly, in situations in which morethan one die is provided on the patterning device MA, the patterningdevice alignment marks may be located between the dies.

The depicted apparatus could be used in at least one of the followingmodes:

1. In step mode, the support structure MT and the substrate table WT arekept essentially stationary, while an entire pattern imparted to theradiation beam is projected onto a target portion C at one time (i.e. asingle static exposure). The substrate table WT is then shifted in the Xand/or Y direction so that a different target portion C can be exposed.In step mode, the maximum size of the exposure field limits the size ofthe target portion C imaged in a single static exposure.

2. In scan mode, the support structure MT and the substrate table WT arescanned synchronously while a pattern imparted to the radiation beam isprojected onto a target portion C (i.e. a single dynamic exposure). Thevelocity and direction of the substrate table WT relative to the supportstructure MT may be determined by the (de-)magnification and imagereversal characteristics of the projection system PL. In scan mode, themaximum size of the exposure field limits the width (in the non-scanningdirection) of the target portion in a single dynamic exposure, whereasthe length of the scanning motion determines the height (in the scanningdirection) of the target portion.

3. In another mode, the support structure MT is kept essentiallystationary holding a programmable patterning device, and the substratetable WT is moved or scanned while a pattern imparted to the radiationbeam is projected onto a target portion C. In this mode, generally apulsed radiation source is employed and the programmable patterningdevice is updated as required after each movement of the substrate tableWT or in between successive radiation pulses during a scan. This mode ofoperation can be readily applied to maskless lithography that utilizesprogrammable patterning device, such as a programmable mirror array of atype as referred to above.

Combinations and/or variations on the above described modes of use orentirely different modes of use may also be employed.

A further immersion lithography solution with a localized liquid supplysystem is shown in FIG. 4. Liquid is supplied by two groove inlets IN oneither side of the projection system PL and is removed by a plurality ofdiscrete outlets OUT arranged radially outwardly of the inlets IN. Theinlets IN and OUT can be arranged in a plate with a hole in its centerand through which the projection beam is projected. Liquid is suppliedby one groove inlet IN on one side of the projection system PL andremoved by a plurality of discrete outlets OUT on the other side of theprojection system PL, causing a flow of a thin film of liquid betweenthe projection system PL and the substrate W. The choice of whichcombination of inlet IN and outlets OUT to use can depend on thedirection of movement of the substrate W (the other combination of inletIN and outlets OUT being inactive).

Another immersion lithography solution with a localized liquid supplysystem solution which has been proposed is to provide the liquid supplysystem with a liquid confinement structure which extends along at leasta part of a boundary of the space between the final element of theprojection system and the substrate table. The liquid confinementstructure is substantially stationary relative to the projection systemin the XY plane though there may be some relative movement in the Zdirection (in the direction of the optical axis). A seal is formedbetween the liquid confinement structure and the surface of thesubstrate. In an embodiment, the seal is a contactless seal such as agas seal. Such a system with a gas seal is disclosed in United Statespatent application no. U.S. Ser. No. 10/705,783, hereby incorporated inits entirety by reference.

FIG. 5 shows a liquid supply system comprising a liquid confinementstructure (sometimes referred to as an immersion hood or showerhead)according to an embodiment of the invention. In particular, FIG. 5depicts an arrangement of a reservoir 10, which forms a contactless sealto the substrate around the image field of the projection system so thatliquid is confined to fill a space between the substrate surface and thefinal element of the projection system. A liquid confinement structure12 positioned below and surrounding the final element of the projectionsystem PL forms the reservoir. Liquid is brought into the space belowthe projection system and within the liquid confinement structure 12.The liquid confinement structure 12 extends a little above the finalelement of the projection system and the liquid level rises above thefinal element so that a buffer of liquid is provided. The liquidconfinement structure 12 has an inner periphery that at the upper endpreferably closely conforms to the shape of the projection system or thefinal element thereof and may, e.g., be round. At the bottom, the innerperiphery closely conforms to the shape of the image field, e.g.,rectangular though this need not be the case.

The liquid is confined in the reservoir by a gas seal 16 between thebottom of the liquid confinement structure 12 and the surface of thesubstrate W. The gas seal is formed by gas, e.g. air, synthetic air, N₂or an inert gas, provided under pressure via inlet 15 to the gap betweenliquid confinement structure 12 and substrate and extracted via outlet14. The overpressure on the gas inlet 15, vacuum level on the outlet 14and geometry of the gap are arranged so that there is a high-velocitygas flow inwards that confines the liquid. It will be understood by theperson skilled in the art that other types of seal could be used tocontain the liquid such as simply an outlet to remove liquid and/or gas.

FIG. 6 shows the different media through which the patterned beam ofradiation will pass according to an embodiment of the invention. Afterleaving the final element FLE (although this element is shown as convex,it may be of other shapes) of the projection system PL, the patternedbeam passes through the immersion liquid 11, a topcoat TC, and into theresist R, which is provided on the substrate W, e.g. by spin coating.Between the resist R and substrate W, an anti-reflection coating (e.g.,a bottom antireflective coating (BARC)) may be provided. The resist R isexposed by the patterned beam and hence is arranged to be sensitive toradiation of the patterned beam, which has a wavelength λ, e.g., 193 nm.Immersion liquid 11 has a refractive index n_(l)>1.6 and is provided toimprove the depth of focus and/or resolution of the image projected ontothe substrate. Topcoat TC is provided (i) to prevent chemical and/orphysical interaction between the immersion fluid 11 and resist R and/or(ii) to keep particulate contaminants and/or nano-particles suspended inthe immersion fluid to increase its refractive index, away from theresist R.

The final element FLE of the projection system may be made of SiO₂, CaF₂BaF₂, Al₂O₃ or a mixture of these and other crystals and so itsrefractive index n_(fle) at 193 nm is 1.5 or higher. Therefore, to avoidinternal reflection in the final element FLE, immersion liquid 11 andtopcoat TC, the thicknesses, d_(l), d_(tc) and d_(r), and refractiveindices, n_(l), n_(tc) and n_(r), of the immersion liquid 11, topcoat TCand resist R meet the following criteria:n _(fle) ≦n _(l) ≦n _(tc) ≦n _(r)  (1)d _(l)≧˜5.λ  (2)d _(tc)≦˜5.λ  (3)

Liquids that can be used as the immersion liquid include: suspensions ofdielectric nano-particles, e.g., alumina; solutions of acids such assulfuric acid or phosphoric acid; and solutions of certain salts such asCe₂SO₄. Therefore, it would be desirable that the topcoat should resistchemical attack from the immersion fluid, especially if the immersionfluid contains sulfuric acid, while not reacting with the resist andbeing immiscible in the resist. It would also be desirable that thetopcoat has physical properties enabling it to be dispensed by a spincoater and remain in a layer of stable thickness as the coated substrateis loaded into the lithographic apparatus. It would also be desirablethat the topcoat is soluble in resist developer as that should avoid aseparate step to remove the topcoat when processing the substrate. Waterbased topcoats, such as TSP3A, TILC-016 and TILC-019 supplied by TokyoOhka Kogyo Co., Ltd., and Teflon based topcoats may be used. Ifnecessary, the refractive index of the topcoat may be increased byadding dielectric nano-particles, having dimensions smaller than thewavelength of the patterned beam, in suspension. The refractive index ofthe topcoat is then a volume average of the refractive index of theparticles and the liquid in which they are suspended. In an embodiment,the dielectric nano-particles have dimensions in the range of from 10 to20 nm. They can be manufactured chemically and encapsulated, e.g. withpolar molecules, to prevent agglomeration into larger particles.

Referring to FIG. 7, in another embodiment of the invention, a thintopcoat with a thickness and refractive index optimized for transmissionis used. The following criteria apply, using the same symbols aspreviously noted:n _(l) ≦n _(tc) ≦n _(r)  (4)d _(l)≧˜5.λ  (5)½.λ≦d _(r)≦λ  (6)

The refractive index of the topcoat should further be made as close aspossible to the square root of the product of the refractive indices ofthe immersion liquid and the resist. A variance of 10% may bepermissible. In other words:n _(tc)=√{square root over (n _(l) .n _(r))}±10%  (7)

An optimum thickness d_(tc) of the topcoat then depends on the numericalaperture, NA, at the substrate and is given by:

$\begin{matrix}{{2 \cdot n_{tc} \cdot d_{tc} \cdot \left( {1 - {\sin^{2}\beta}} \right)} = {{\left( {m - \frac{1}{2}} \right)\lambda}{where}}} & (8) \\{{{\sin\;\beta} = {{{{NA} \cdot \frac{n_{l}}{n_{r}}}{and}\mspace{14mu} m} = 1}},2,3,{{etc}.}} & (9)\end{matrix}$Again, a variance of 10% may be permissible.

FIG. 8 is a view, similar to FIG. 7, of different media through whichthe patterned beam of radiation will pass according to anotherembodiment of the invention. This embodiment is the same as theembodiment(s) described in relation to FIG. 6 and FIG. 7 except that aprimer layer 20 is provided between the resist R and topcoat TC. Theprimer layer 20 is intended to promote adhesion, e.g., by matchingsurface characteristics, between the resist R and the topcoat TC and itsexact composition will depend on the materials used as the resist andtopcoat. The primer layer may also prevent or reduce diffusion betweenthe topcoat and the resist layer in either direction. The primer layer20 should be as thin as possible, and, in an embodiment, much thinnerthan the wavelength of the exposure radiation so as to minimize itseffect on imaging.

Where layer thicknesses are defined in terms of the wavelength ofradiation of the patterned beam, the wavelength is to be taken as thewavelength in the respective medium.

In European Patent Application No. 03257072.3, the idea of a twin ordual stage immersion lithography apparatus is disclosed. Such anapparatus is provided with two tables for supporting a substrate.Leveling measurements are carried out with a table at a first position,without immersion liquid, and exposure is carried out with a table at asecond position, where immersion liquid is present. Alternatively, theapparatus has only one table.

Although specific reference may be made in this text to the use oflithographic apparatus in the manufacture of ICs, it should beunderstood that the lithographic apparatus described herein may haveother applications, such as the manufacture of integrated opticalsystems, guidance and detection patterns for magnetic domain memories,flat-panel displays, liquid-crystal displays (LCDs), thin-film magneticheads, etc. The skilled artisan will appreciate that, in the context ofsuch alternative applications, any use of the terms “wafer” or “die”herein may be considered as synonymous with the more general terms“substrate” or “target portion”, respectively. The substrate referred toherein may be processed, before or after exposure, in for example atrack (a tool that typically applies a layer of resist to a substrateand develops the exposed resist), a metrology tool and/or an inspectiontool. Where applicable, the disclosure herein may be applied to such andother substrate processing tools. Further, the substrate may beprocessed more than once, for example in order to create a multi-layerIC, so that the term substrate used herein may also refer to a substratethat already contains multiple processed layers.

The terms “radiation” and “beam” used herein encompass all types ofelectromagnetic radiation, including ultraviolet (UV) radiation (e.g.having a wavelength of or about 365, 248, 193, 157 or 126 nm).

The term “lens”, where the context allows, may refer to any one orcombination of various types of optical components, including refractiveand reflective optical components.

While specific embodiments of the invention have been described above,it will be appreciated that the invention may be practiced otherwisethan as described. For example, the invention may take the form of acomputer program containing one or more sequences of machine-readableinstructions describing a method as disclosed above, or a data storagemedium (e.g. semiconductor memory, magnetic or optical disk) having sucha computer program stored therein.

One or more embodiments of the present invention may be applied to anyimmersion lithography apparatus, such as those types mentioned above,and whether the immersion liquid is provided in the form of a bath oronly on a localized surface area of the substrate. A liquid supplysystem is any mechanism that provides a liquid to a space between theprojection system and the substrate and/or substrate table. It maycomprise any combination of one or more structures, one or more liquidinlets, one or more gas inlets, one or more gas outlets, and/or one ormore liquid outlets, the combination providing and confining the liquidto the space. In an embodiment, a surface of the space may be limited toa portion of the substrate and/or substrate table, a surface of thespace may completely cover a surface of the substrate and/or substratetable, or the space may envelop the substrate and/or substrate table.

The descriptions above are intended to be illustrative, not limiting.Thus, it will be apparent to one skilled in the art that modificationsmay be made to the invention as described without departing from thescope of the claims set out below.

1. A device manufacturing method, comprising: projecting a patternedbeam of radiation through a liquid onto a resist provided on asubstrate, wherein a topcoat layer is provided between the resist andthe liquid, the topcoat comprising a suspension of nano-particles. 2.The method according to claim 1, wherein the nano-particles havedimensions in the range of about 10 to 20 nanometers.
 3. The methodaccording to claim 1, wherein the topcoat has a refractive index ofgreater than or equal to about 1.6.
 4. The method according to claim 1,wherein the topcoat has a refractive index of greater than or equal toabout 1.7.
 5. The method according to claim 1, wherein the suspension ofparticles comprises a suspension of dielectric nano-particles.
 6. Themethod according to claim 1, wherein the particles have dimensions lessthan the wavelength of the radiation of the patterned beam.
 7. Themethod according to claim 1, wherein the liquid has a refractive indexgreater than or equal to a refractive index of the topcoat.
 8. Themethod according to claim 1, wherein the topcoat has a refractive indexgreater than or equal to a refractive index of the resist.
 9. The methodaccording to claim 1, wherein the topcoat layer has a thickness that isless than or equal to about five times the wavelength of the radiationof the patterned beam.
 10. The method according to claim 1, furthercomprising a primer layer provided between the resist and the topcoatlayer, the primer layer having a thickness less than the wavelength ofthe radiation of the patterned beam.
 11. A device manufacturing method,comprising: projecting a patterned beam of radiation through a liquidonto a resist provided on a substrate, wherein a topcoat layer isprovided between the resist and the liquid and a primer layer isprovided between the resist and the topcoat, the primer layer having athickness less than the wavelength of the radiation of the patternedbeam.
 12. The method according to claim 11, wherein the primer layerpromotes adhesion of the topcoat to the resist.
 13. The method accordingto claim 11, wherein the topcoat comprises a suspension ofnano-particles.
 14. A device manufacturing method, comprising:projecting a patterned beam of radiation through a liquid onto a resistprovided on a substrate, wherein a topcoat layer is provided between theresist and the liquid, the topcoat layer having a thickness that is lessthan or equal to about five times the wavelength of the radiation of thepatterned beam, the liquid has a thickness that is greater than or equalto about five times the wavelength of the radiation of the patternedbeam, and the liquid, the topcoat and the resist have respectively,first, second and third refractive indices, the first refractive indexbeing less than or equal to the second refractive index and the secondrefractive index being less than or equal to the third refractive index.15. The method according to claim 14, wherein the patterned beam isprojected using a projection system and the projection system has afinal element which has a fourth refractive index, the first refractiveindex being larger than or equal to the fourth refractive index.
 16. Themethod according to claim 14, wherein the first refractive index isgreater than or equal to about 1.6.
 17. The method according to claim14, wherein the first refractive index is greater than or equal to about1.7.
 18. The method according to claim 14, wherein the topcoat comprisesa suspension of dielectric nano-particles having dimensions less thanthe wavelength of the radiation of the patterned beam.
 19. The methodaccording to claim 18, wherein the nano-particles have dimensions in therange of about 10 to 20 nanometers.
 20. The method according to claim 1,wherein the topcoat comprises a suspension of nano-particles.
 21. Themethod according to claim 1, further comprising a primer layer providedbetween the resist and the topcoat layer, the primer layer having athickness less than the wavelength of the radiation of the patternedbeam.
 22. A device manufacturing method, comprising: projecting apatterned beam of radiation through a liquid onto a resist provided on asubstrate, wherein a topcoat layer is provided between the resist andthe liquid, the topcoat has a thickness substantially equal to$\frac{\left( {m - \frac{1}{2}} \right)\lambda}{2 \cdot n_{tc} \cdot \left( {1 - {\sin^{2}\beta}} \right)},$wherein ${{\sin\;\beta} = {{NA} \cdot \frac{n_{l}}{n_{r}}}},$ m =1, 2,3, etc.,λ is the wavelength of the radiation of the patterned beam, NAis the numerical aperture at the substrate, n₁ is the refractive indexof the liquid, n_(tc) is the refractive index of the topcoat, and n_(r)is the refractive index of the resist; the liquid has a thickness thatis greater than or equal to about five times λ, the resist has athickness in the range of from half to one times λ, and n₁ is less thanor equal to n_(tc), n_(tc) is less than or equal to n_(r), and n_(tc) isabout equal to the square root of the product of n₁ and n_(r).
 23. Themethod according to claim 22, wherein the patterned beam is projectedusing a projection system and the projection system has a final elementhaving a refractive index less than or equal to n₁.
 24. The methodaccording to claim 22, wherein n₁ is greater than about 1.6.
 25. Themethod according to claim 22, wherein n₁ is greater than about 1.7. 26.The method according to claim 22, wherein the topcoat comprises asuspension of dielectric nano-particles having dimensions less than λ.27. The method according to claim 26, wherein the nano-particles havedimensions in the range of about 10 to 20 nanometers.